// Assume roles with no JWT, handles AssumeRole.
	stsRouter.Methods(http.MethodPost).MatcherFunc(func(r *http.Request, rm *mux.RouteMatch) bool {
		ctypeOk := wildcard.MatchSimple("application/x-www-form-urlencoded*", r.Header.Get(xhttp.ContentType))
		authOk := wildcard.MatchSimple(signV4Algorithm+"*", r.Header.Get(xhttp.Authorization))
		noQueries := len(r.URL.RawQuery) == 0
		return ctypeOk && authOk && noQueries

	if err != nil {
		return "", fmt.Errorf("new request err (/login): %v", err)
	}
	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
	_, err = dexClient.Do(req)
	if err != nil {
		return "", fmt.Errorf("post form err: %v", err)
	}
	// fmt.Printf("resp: %#v %#v\n", resp.StatusCode, resp.Header)
	// bodyBuf, err := io.ReadAll(resp.Body)